An improved vehicle transmission shift control mechanism having a service brake and shift lever interlock system is described in copending U.S. Pat. application Ser. No. 314,717 filed Feb. 23, 1989, of common assignee herewith.
The interlock system described in that patent application includes a shift lever pivotal between a "Park" position and other operative positions such as drive, reverse, neutral, etc. The shift lever is selectively retained in one of these positions by a detent mechanism which releasably couples the shift lever and a detent plate. The detent mechanism is manually released out of coupling relation between the detent plate and shift lever to free the shift lever for repositioning.
An electromechanical mechanism, including a solenoid and a pivotal bellcrank locking lever connected to an ignition mechanism via an actuating cable, is employed to control locking/unlocking of the shift lever in the "Park" position in response to the operational mode of the service brake system of the vehicle. In particular, a service brake responsive switch is employed in combination with other switches, such as the ignition switch and shift lever position responsive switch, to control locking/unlocking of the shift lever in the "Park" position when the ignition switch is in the "Start" or "Run" position. These switches are employed in a logic control circuit in such a manner that the shift lever is locked in the "Park" position when the ignition switch is closed (e.g., in the "Start" or "Run" position) and the service brake pedal is in the brake released mode. The logic control circuit does not effect locking of the shift lever under other conditions or positions of these components.
It is an object of the present invention to provide a shift lever interlock system for a vehicle which eliminates the need for a bellcrank locking lever and associated mechanical components, especially the cable that connects the bellcrank locking lever to the ignition mechanism of the vehicle.
It is another object of the invention to provide such a shift lever interlock system which interlocks the shift lever electronically with ignition circuit, ignition key-in, service brake system, and battery system input signals such that the shift lever is locked in the "Park" position unless the ignition key is inserted or the ignition switch is unlocked and the service brake system is in a brake applied mode or unless the battery voltage level is below a predetermined level.
It is a further object of the present invention to provide a shift lever interlock system having a bidirectional interlock actuator providing self-generated extend and retract signals which are logically combined with the aforementioned other vehicle inputs such that the interlock actuator is actuable until the extend position (corresponding to shift lever locking) or the retract position (corresponding to shift lever unlocking) is reached and remains at rest at one of these positions until reactuated to move to the other of these positions.
It is a further object of the invention to provide a shift lever interlock system wherein the shift lever position, battery voltage level, ignition key-in, ignition circuit and service brake system are monitored for input to the logic control circuitry of the interlock system.
It is a further object of the invention to provide a shift lever interlock system wherein a locking member or plunger of the interlock actuator resides beneath the "Park" detent when moved to the extend position to lock the shift lever in the "Park" position to insure the interlock system functions only with respect to the "Park" position and not other positions of the shift lever.